1. Field of the Invention
The present invention broadly relates to a paper sizing composition which may be used with uncoated or single-side coated paper webs. The present invention also broadly relates to paper webs treated on one or both sides with a paper surface sizing composition to impart benefits relating to one or more of the following properties: (1) brightness; (2) opacity; (3) paper smoothness; (4) print quality; (5) optionally ink dry time (e.g., for ink jet printing where the sizing composition has option); and (6) optionally minimizing or eliminating edge welding (e.g., for paper webs used in, for example, form printing). The present invention further broadly relates a method for treating one or more sides of an uncoated or a single-side coated paper web with a paper surface sizing composition.
2. Related Art
Conventional papermaking for calendered papers involves formation of a web of fibers on a papermaking machine using, for example, a moving porous foraminous support wherein water is drained from a dilute slurry of fibers deposited on the support. Additional water removal from the web may be achieved by using, for example, a press roll section, with final removal of water occurring, for example, in a dryer section of the papermaking machine.
In a conventional calendered papermaking process, the fibrous web from the press roll section may contains about 32 to about 45 wt. % solids. These solids may include wood pulp and/or synthetic fibers along with various additives such as sizing agents, binders, fillers, pigments, etc. The print quality of such calendared papers, as well as other properties of the papers, such as brightness, opacity, paper smoothness, etc., may be improved by coating the paper with different coating compositions. Coated papers refer to paper products to which at least 8 grams per square meter (gsm) of coating color solids have been applied to at least one surface of the paper web at a coating station. The coating composition used to provide these color solids may comprise a mixture of: (1) a coating color having pigment(s) such as clay, calcium carbonate, titanium dioxide, etc., (2) a binder or binders such as modified starch, styrene butadiene rubber, polyvinyl acetate, vinyl acrylic, polyvinyl alcohol, etc.; and (3) various functional additives such as dispersants, viscosity modifiers, crosslinking agents, lubricants, etc. The resulting mixture may be applied to the paper web at a solids content of, for example, about 40% or greater by weight.
These coated papers may be used for a wide range of products including packaging, art paper, brochures, magazines, catalogues, leaflets, etc. Such coated paper may provide a range of desirable properties, including brightness, opacity, sheet gloss, printing performance, etc. While these coated papers have the above described desirable paper properties, these properties are often achieved at a significant increase in cost relative to uncoated papers.
By contrast, uncoated papers may be defined as any paper product which has 0 to 8 grams per square meter (gsm) of a starch or starch/pigment mixture solids applied to one or both sides of the paper web, but which does not undergo subsequent surface application as described above for coated papers. Uncoated papers also may or may not undergo treatment at the size press. If a starch or starch-pigment mixture is applied at the size press, the solids content of the mixture for uncoated paper will be less than for coated papers, e.g., less than about 40% by weight. While uncoated papers are significantly less expensive compared to coated papers, uncoated papers also may not have the properties desired in coated papers, for example, brightness, opacity, paper smoothness, print quality, etc.
Accordingly, it would be desirable to be able to provide in coated paper properties, such as brightness, opacity, paper smoothness, print quality, etc., with a cost that is less than that of the typical cost of coated paper.